High-strength pipeline wide and thick steel plate based on strain design and production method thereof

Abstract

The invention discloses a high-strength pipeline wide and thick steel plate based on strain design and a production method thereof. The steel plate comprises the following chemical components in percentage by weight: 0.030%-0.065% of C, 0.20%-0.45% of Si, 1.70%-1.85% of Mn, less than 0.030% of Nb, 0.060%-0.15% of V, 0.075%-0.170% of (Nb + V), 0.005%-0.025% of Ti, less than or equal to 2.0 of Ti / N, and Nilt. The steel comprises the following components in percentage by weight: 0.15% of Fe, less than 0.15% of Mo, 0.20%-0.50% of Cr, less than 0.15% of Cu, 0.40%-0.80% of (Ni + Mo + Cr + Cu), less than or equal to 0.025% of Zr, 0.005%-0.025% of Al, 0.005%-0.015% of N, 0.0015%-0.0040% of Ca, more than or equal to 1.6% of Ca / S, less than or equal to 0.010% of P, less than or equal to 0.002% of S, less than or equal to 0.00015% of H, less than or equal to 0.0018% of O and the balance of iron and inevitable impurities. The CEIIW of the high-strength pipeline wide and thick steel plate is controlled to be 0.42%-0.49%, the CEPcm of the high-strength pipeline wide and thick steel plate is controlled to be 0.17%-0.21%, the high-strength pipeline wide and thick steel plate with high strength, high toughness, strain resistance and good weldability is obtained through specific heating, rolling and cooling production processes, and the high-strength pipeline wide and thick steel plate has very wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of low alloy steel, and in particular relates to a high-strength pipeline wide and thick steel plate based on strain design with a thickness of ≥30 mm, high strength, high toughness, good strain resistance and weldability, and a production method thereof. Background Art

[0002] As oil and gas resources in conventional regions decrease, oil and gas extraction continues to expand into geologically and environmentally complex regions, such as the polar regions, oceans, high-altitude cold regions, and geologically active areas. The demand for high-strength pipeline steel plates for service in complex regions is becoming increasingly urgent, becoming a major bottleneck in long-distance pipeline construction. To meet service needs in complex areas, strain-based high-strength pipeline steel plates must exhibit excellent strain characteristics, such as high uniform elongation, high stress ratio, and low yield ratio. At the same time, to ensure pipeline operation safety and efficient transportation capacity, the steel plates must possess comprehensive technical characteristics such as good transverse and longitudinal strength, high toughness, and thick wall and large plate width specifications. Furthermore, such products are prone to embrittlement and softening in the heat-affected zone after welding, resulting in reduced strength and hardness, which directly affects service safety. Therefore, they must possess excellent weldability. The complex and diverse technical requirements significantly increase the difficulty of designing and manufacturing thick-walled, high-strength pipeline steel plates designed based on strain.

[0003] Patent publication number CN109234623B, "An X80M Deep-Sea Strain-Resistant Pipeline Steel Plate and Rolling Process," provides an X80-grade deep-sea pipeline steel plate. This design utilizes a high nickel (0.65% to 0.85%) and high molybdenum (0.31% to 0.36%) composition, resulting in excessively high alloy content and cost. Patent publication number JP2021155823A, "Method for Manufacturing Low-Yield Ratio High-Strength Steel Plate," provides a steel plate with a tensile strength of 550-650 MPa, insufficient to meet the requirements of X80-grade strain-designed pipeline steel. In summary, existing research on strain-designed, thick-walled, high-strength pipeline steel plates and their production technologies remains insufficient, particularly those with the combined technical characteristics of high strength, high toughness, strain resistance, and good weldability. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a high-strength pipeline wide and thick steel plate based on strain design with a thickness of ≥30 mm, high strength, high toughness, good strain resistance and weldability, and a production method thereof. The high-strength pipeline wide and thick steel plate based on strain design described in the present invention is based on C, Mn, V, Cr, and Si. The basic tensile strength is guaranteed by the addition of Mn, Cr, and Si, and the polygonal ferrite phase transformation is promoted by the low Nb and Mo design, while reducing the alloy cost; moreover, low Nb can reduce the inhibition of V precipitates and give full play to the role of V; through the composite addition of V, C, and N and the control of Al and Ti content, an appropriate amount of carbonitride precipitation is obtained, on the one hand, promoting phase deformation nucleation and grain refinement, which is particularly beneficial to improving the microstructure and performance uniformity of the thick section of the thick-walled pipeline steel plate; on the other hand, it exerts the precipitation strengthening effect; effectively inhibits welding embrittlement and softening; and controls inclusions by adding elements such as Zr and Ca, which plays a beneficial role in the phase transformation and welding process. The toughness is improved by reducing the P, S, H, and O contents and controlling the quality of the continuous casting billet; and the production processes such as smelting, heating, rolling and cooling that match the alloy composition are used to enable the steel plate to obtain comprehensive technical characteristics such as high strength, high toughness, strain resistance, good weldability and large wall thickness, as well as ideal microstructure.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a high-strength pipeline wide and thick steel plate based on strain design, the chemical composition and its weight percentage are C: 0.030% to 0.065%, Si: 0.20% to 0.45%, Mn: 1.70% to 1.85%, Nb < 0.030%, V: 0.060% to 0.15%, (Nb+V): 0.075% to 0.170%, Ti: 0.005% to 0.025%, Ti / N ≤ 2.0, Ni < 0.15%, Mo < 0.15%, Cr: 0.20% ~ 0.50%, Cu < 0.15%, (Ni + Mo + Cr + Cu): 0.40% ~ 0.80%, Zr ≤ 0.025%, Al: 0.005% ~ 0.025%, N: 0.005% ~ 0.015%, Ca: 0.0015% ~ 0.0040%, Ca / S ≥ 1.6, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0018%, the balance is iron and unavoidable impurities.

[0007] Based on the above technical solution, further, the high-strength pipeline wide and thick steel plate CE based on strain design IIW Controlled at 0.42% to 0.49%, CE Pcm Controlled at 0.17% to 0.21%, among which

[0008] CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15;

[0009] CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0010] Based on the above technical solution, further, Ti / N: 0.6~1.9, (Ni+Mo+Cr+Cu): 0.40%~0.70%, Ca / S: 1.7~3.5.

[0011] The reasons for the composition design of the present invention are as follows:

[0012] Carbon (C) is a fundamental element for increasing strength, acting through both alloy carbide precipitation and interstitial solid solution. In addition to utilizing C's solid solution strengthening properties, the present invention leverages C's ability to form fine precipitations with V and other elements during the steel plate's medium-temperature deformation, slow cooling, and welding processes. This, in turn, promotes phase nucleation, refines the structure, increases strength, and reduces softening in welded joints. Furthermore, C significantly improves hardenability and tensile strength, contributing to a lower yield strength ratio and improved strain performance. However, increased carbon content negatively impacts plasticity and toughness. In the present invention, a C content of 0.030% to 0.065% is ideal.

[0013] Si improves hardenability and strength, and is beneficial to increasing the strain hardening rate. At the same time, to create favorable conditions for VN precipitation, the present invention strictly controls the Al content and utilizes Si to partially replace Al to play the role of a deoxidizer. However, too high a Si content will increase the M / A in the structure and reduce toughness and plasticity. In the present invention, the suitable range of Si is 0.20% to 0.45%.

[0014] Mn is a major strengthening element that can improve hardenability and facilitate homogenization of the microstructure of thick-walled steel plates. Furthermore, Mn is inexpensive and can improve the economic efficiency of the product. However, excessively high manganese content can easily induce segregation and lower the phase transformation temperature, hindering the formation of soft-phase ferrite and thus affecting strain resistance. In the present invention, the Mn content is controlled within a range of 1.70% to 1.85%.

[0015] Nb can form fine Nb(CN) precipitation under appropriate processes, which has a grain-refining effect and can improve strength and toughness. However, if the Nb content is too high, on the one hand, it is necessary to increase the heating temperature of the continuous casting billet to ensure the solid solution effect, and on the other hand, it will increase the austenite recrystallization temperature, requiring the use of higher temperature rolling. At the same time, it will also inhibit the formation of V-containing precipitation phases. In the present invention, the Nb content is controlled to below 0.030%.

[0016] V has solid solution and precipitation effects and has a strong tendency to combine with C and N. It can combine with C and N to form fine precipitation during rolling, cooling, and welding, refine the grains, promote ferrite nucleation during austenite transformation, facilitate the acquisition of polygonal ferrite, and improve the microstructural uniformity of the steel plate thickness cross-section. At the same time, V can improve the toughness and hardness of welded joints and prevent or reduce welding softening. However, excessive V content is detrimental to toughness and weldability. Therefore, in the present invention, V is controlled to 0.060% to 0.15%.

[0017] Controlling Nb+V within the range of 0.075% to 0.170% is beneficial to ensuring the fine dispersion of the precipitated phase and preventing the precipitated phase from growing excessively; at the same time, it is beneficial to controlling the microstructure and alloy cost.

[0018] Ti easily forms a Ti(CN) precipitate phase with a relatively high solid solution temperature, inhibiting the grain growth of austenite under high temperature conditions. Furthermore, Ti can refine the weld structure and improve the toughness of the heat-affected zone after welding. Furthermore, Ti has the effect of fixing oxygen. However, excessive Ti and Ti / N ratios increase the size of precipitates and inhibit the formation of Nb- and V-containing precipitates. In the present invention, the Ti content is controlled to 0.005% to 0.025%, and the Ti / N ratio is ≤2.0.

[0019] Ni can increase strength, delay pearlite transformation, facilitate microstructure control and grain refinement, improve low-temperature toughness, and reduce Cu brittleness; however, Ni is relatively expensive and should not be added excessively; therefore, the Ni content in the present invention is controlled below 0.15%.

[0020] Mo can improve hardenability, promote low-temperature microstructure transformation, has a certain grain refining effect, and can also improve post-weld strength and hardness; however, too high a molybdenum content will inhibit ferrite transformation, which is not conducive to multiphase microstructure and strain performance control; at the same time, Mo is relatively expensive, and adding too much will significantly increase costs. Therefore, the present invention controls the Mo content to below 0.15%.

[0021] Cr can increase hardenability and improve tensile strength, which is beneficial to improving the uniformity of the microstructure in the thickness direction. Moreover, it has a weaker inhibition on the transformation of austenite to polygonal ferrite, which is beneficial to increasing the "hardness difference" between the soft / hard phases in the microstructure, facilitating the control of strain resistance and yield ratio. Moreover, Cr, as an inexpensive element, can replace precious alloying elements such as Mo, Ni, and Cu, effectively reducing costs. However, excessive Cr content increases weld crack sensitivity. Therefore, the present invention controls the Cr content to 0.20% to 0.50%.

[0022] Cu improves hardenability, increases hardness and tensile strength of hard phase structure, and improves cooling effect of thick-walled steel plate. However, too high Cu content is detrimental to toughness. In the present invention, the Cu content is controlled to be less than 0.15%.

[0023] Controlling the (Ni+Mo+Cr+Cu) content at 0.40%-0.80% can ensure hardenability and strengthening effects. At the same time, it is beneficial to phase transformation and microstructure control and improves strain properties.

[0024] Zr is a strong deoxidizing element. The present invention utilizes Zr oxides formed by the combination of Zr and oxygen. Zr oxides have a small density difference with molten steel, making them easily dispersed. Furthermore, Zr oxides in molten steel carry an electric charge and possess a certain degree of conductivity, making them less likely to aggregate and grow. This facilitates the fine, dispersed distribution of Zr oxides in the steel, promoting phase nucleation, grain refinement, and improved performance. Furthermore, Zr can refine the microstructure of the weld heat-affected zone and improve toughness. Furthermore, Zr's interaction with oxygen can reduce the interaction between V and oxygen, promoting V precipitation. However, excessive Zr content reduces toughness. Therefore, in the present invention, Zr is set to ≤ 0.025%.

[0025] Al has a strong affinity with O and N and is a deoxidizing element. However, an excessively high Al content will promote the increase of Al-containing inclusions and the reduction of free N, affecting the formation of precipitates such as VN. In the present invention, the Al content is preferably controlled within a range of 0.005% to 0.025%.

[0026] N: The present invention utilizes N to form fine precipitates with V, Nb, and Ti to exert strengthening and grain refinement effects, thereby improving strength, toughness, and weld joint performance. However, excessive N content deteriorates toughness and may also cause quality defects in the steel plate. The content is preferably controlled within a range of 0.005% to 0.015%.

[0027] Ca and Ca / S can promote the denaturation and spheroidization of inclusions, and reduce the adverse effects of inclusions on plasticity and toughness. In the present invention, Ca is 0.0015% to 0.0040%, and Ca / S is ≥1.6.

[0028] P and S are harmful impurity elements in the present invention. P will reduce toughness, so the present invention controls P to ≤ 0.010%. An increase in S content will promote the formation and growth of inclusions and destroy the continuity of the matrix, so S is ≤ 0.002%.

[0029] Increased H and O contents will lead to decreased toughness, increased inclusions, and reduced performance. Therefore, the present invention controls H≤0.00015% and O≤0.0018%.

[0030] The present invention CE IIW Controlled at 0.42% to 0.49%, CE Pcm Controlling it within 0.17% to 0.21% can not only meet the strength and toughness requirements of the steel plate, but also reduce the tendency of welding cracking, making the steel plate have good weldability.

[0031] Based on the above technical solution, further, the thickness of the high-strength pipeline wide and thick steel plate based on strain design is ≥30mm, the microstructure is polygonal ferrite + lath bainite and a small amount of granular bainite, the volume percentage of polygonal ferrite is 20-80%, the grain size is 4-10μm, and fine precipitation with a particle size of <20nm is dispersed in the matrix. The transverse yield strength reaches 490-570MPa, the transverse tensile strength reaches 680-770MPa, the transverse yield ratio is <0.78, the average transverse impact energy at -60℃ is ≥220J, the average transverse impact energy at -20℃ in the welding heat affected zone is ≥180J, and the transverse DWTT shear area at -25℃ is ≥85%; the longitudinal yield strength reaches 450-550MPa, the longitudinal tensile strength reaches 660-760MPa, and the longitudinal uniform elongation U EL ≥12%, longitudinal yield strength ratio <0.77, longitudinal stress ratio Rt 1.5 / Rt 0.5 ≥1.12, Rt 2.0 / Rt 1.0 ≥1.06.

[0032] The present invention also provides a method for producing the above-mentioned high-strength pipeline wide and thick steel plate based on strain design, comprising the following steps:

[0033] (1) Heating: The continuous casting billet is heated in multiple stages, including preheating, heating, and soaking. The furnace temperature is 1100-1160°C, and the total heating time is 1.0-2.0 min / mm.

[0034] (2) Rolling: including rough rolling and finishing rolling. Rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The starting temperature of rough rolling is 1070-1130°C, the finishing temperature of rough rolling is 980-1030°C, and the total reduction rate of rough rolling is ≥60%. Among them, the last 2-3 passes of rough rolling stage 1, intermediate cooling, and rough rolling stage 2 are all cooled by rapid spray water, with an average cooling rate of ≥1°C / s. The starting temperature of rough rolling stage 2 is below 1050°C, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases gradually from pass to pass, and the rough rolling speed is 1.0-2.0 m / s.

[0035] After the rough rolling is completed, the intermediate warm billet is rapidly cooled to 850-900°C with an average cooling rate of ≥2°C / s, and then warmed to the start temperature of finishing rolling. The deformation rate in the finishing rolling stage is 60-75%, the start temperature of finishing rolling is 790-840°C, and the final rolling temperature of finishing rolling is Ar3±20°C, where Ar3=910-273*C-74*Mn-57*Ni-16*Cr-58*Mo-18*Cu;

[0036] (3) Cooling: The steel plate is air-cooled for a time of t after rolling. After air cooling, it is pre-straightened and then subjected to two-stage water cooling. The average cooling rate in the first stage is 10-20°C / s, and the average cooling rate in the second stage is 3-10°C / s. The end temperature of water cooling is <250°C.

[0037] Based on the above technical solution, further, in step (2), the total deformation rate of the second rough rolling stage is 30-50%.

[0038] Based on the above technical solution, further, the finishing rolling temperature in step (2) is 730-760°C.

[0039] Based on the above technical solution, further, in step (3), the air cooling time t = (FRT-Ar3) / a+k*h, t is the air cooling time, s; FRT is the final rolling temperature, ℃; a is a coefficient related to the cooling rate, ranging from 0.4 to 1.0℃ / s; k is a coefficient, ranging from 0.9 to 2.0s / mm, h is the thickness of the steel plate in mm; the water cooling end temperature is 100 to 200℃.

[0040] Based on the above technical scheme, further, the preparation of the continuous casting billet described in step (1) includes converter smelting, refining outside the furnace and continuous casting; the converter tapping temperature of the converter smelting is ≤1640℃, the tapping C is ≤0.045%, the slag is blocked for tapping, and the slag layer thickness is ≤40mm; Ti is added first after refining and deoxidation, and then Zr and V are added; the calming time of the molten steel before being put on the machine after refining outside the furnace is ≥10min; the continuous casting billet pouring overheating during the continuous casting process is 10~40℃, the residence time of the molten steel in the ladle during pouring is ≥350s, the dynamic light reduction of the billet is ≥4mm, and the continuous casting adopts a constant pulling speed, and the pulling speed control range is 0.6~1.2m / min.

[0041] Based on the above technical solution, further, lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag during the converter smelting process, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

[0042] Based on the above technical solution, further, the center segregation of the continuous casting billet is ≤C0.5 level, the center porosity is ≤0.5 level, and A / B / C / D type inclusions are controlled within level 1.

[0043] The present invention adopts the above-mentioned production method for the following reasons:

[0044] The low-carbon, low-temperature, and slag-blocking tapping of the converter can effectively control the carbon content of the final product, ensure the dephosphorization effect, and reduce rephosphorization and resulfurization; the production of white slag and the control of FeO+MnO in the slag can ensure the reducing ability of the slag, fully desulfurize, reduce inclusions, and improve cleanliness;

[0045] The order of adding Ti, Zr and V after refining and deoxidation can more effectively improve the yield and efficiency of the corresponding elements; the control of quenching, pouring superheat and residence time in the tundish before the molten steel is put into the machine can homogenize the molten steel temperature and effectively promote the floating and removal of inclusions; the control of dynamic soft reduction and continuous casting billet drawing speed can effectively improve the quality of the billet and reduce defects such as cracks and segregation. The control of center segregation, center porosity and inclusions is an effective guarantee for the quality of the continuous casting billet and the performance of the steel plate.

[0046] The multi-stage heating of the continuous casting billet and the control of the total heating time are beneficial to improving the heating efficiency and uniformity; since the Nb content in the present invention is low, the element solid solution requirement can be met by adopting low-temperature heating out of the furnace, and at the same time, the austenite grain size can be effectively reduced. Moreover, it is more conducive to lowering the rough rolling temperature, reducing the rolling time in the rough rolling stage, and realizing efficient low-temperature rolling.

[0047] The present invention's rough rolling process primarily utilizes a low-temperature rolling process combined with high-temperature-gradient deformation across the thickness of the steel. Because the V-containing and low-Nb design of the present invention reduces the austenite recrystallization temperature, low-temperature rolling is used during the rough rolling stage to recrystallize the austenite grains and effectively inhibit grain growth. Multi-stage rapid cooling significantly increases the temperature gradient across the thickness of the steel, while low-temperature, low-speed rolling in the second rough rolling stage promotes the penetration of rolling deformation toward the center of the thickness of the ingot. This, combined with the effects of V, refines the microstructure near the thickness center, improving the microstructure and performance uniformity of thick-gauge steel plates. The use of a progressively increasing deformation rate in the second rough rolling stage promotes sufficient recrystallization of the austenite.

[0048] The deformation rate in the finishing rolling stage can ensure the deformation and flattening of austenite in the unrecrystallized zone of the finishing rolling while taking into account the distribution of the deformation rates of roughing and finishing rolling. The rapid cooling of the intermediate warm billet after roughing rolling can quickly reduce the temperature and effectively inhibit the growth of austenite. The low temperature and critical phase transformation temperature rolling in the finishing rolling stage are used. On the one hand, it is conducive to the formation of substructures and the accumulation of deformation energy in the microstructure. On the other hand, it can promote the formation of a small amount of deformation-induced ferrite, improving plasticity, toughness and strain. It also provides good thermodynamic and kinetic conditions for the precipitation of V(CN) and Nb(CN), thereby playing the role of grain refinement, pinning, and promoting phase deformation nucleation. Post-rolling air cooling is beneficial to controlling the polygonal ferrite phase transformation and further precipitation of precipitates. Pre-straightening of the steel plate is beneficial to improving the uniformity of water cooling and ensuring the flatness of the steel plate. The use of a low final cooling temperature can form a high-hardness microstructure dominated by bainite. The use of a segmented water cooling process with fast cooling at the beginning and slow cooling at the end can increase the cooling rate in the high-temperature section and inhibit high-temperature phase transformation. At the same time, the smaller cooling water volume in the low-temperature section can reduce internal stress and improve the shape of the plate after cooling.

[0049] The present invention has the following beneficial effects compared to the prior art:

[0050] (1) The steel plate composition of the present invention is based on C, Mn, V, Cr, and Si. By adding V, C, and N in combination and controlling the content of Al and Ti, an appropriate amount of carbonitride precipitation is obtained. On the one hand, it promotes phase deformation nucleation and grain refinement, which is particularly beneficial to improving the microstructure and performance uniformity of the thick section of thick-walled pipeline steel plates; on the other hand, it plays a precipitation strengthening role; in addition, it effectively suppresses welding embrittlement; by reducing the addition of Nb and Mo, polygonal ferrite phase transformation is promoted, and at the same time, the alloy cost is reduced; moreover, reducing Nb can reduce the inhibition of V precipitation and give full play to the role of V; by adding elements such as Zr and Ca to control inclusions, a beneficial role is played in the phase transformation and welding process; by reducing the content of P, S, H, and O and controlling the quality of continuous casting billets, etc., toughness is improved; and by using production processes such as smelting, heating, rolling and cooling that match the alloy composition, the steel plate obtains comprehensive technical characteristics such as high strength, high toughness, strain resistance, good weldability and large wall thickness and an ideal microstructure.

[0051] (2) Based on the composition design of the present invention, the production methods of low-temperature heating, rough rolling multi-stage high temperature gradient deformation of thickness section + low-temperature rolling, rapid cooling of intermediate warm billet after rough rolling, finishing low-temperature critical deformation, post-rolling air cooling and multi-stage water cooling based on rolling temperature and steel plate thickness control are adopted to obtain a microstructure of polygonal ferrite + lath bainite, which can also include a small amount of granular bainite, and dispersed fine precipitation. The proportion of each phase, the size and distribution of the precipitate phase are ideally controlled, which plays an important role in obtaining good comprehensive performance of the steel plate.

[0052] (3) The thickness of the high-strength pipeline wide and thick steel plate based on strain design described in the present invention is ≥30mm, the transverse yield strength can reach 490-570MPa, the transverse tensile strength reaches 680-770MPa, the transverse yield strength ratio is <0.78, the average transverse impact energy at -60℃ is ≥220J, the average transverse impact energy at -20℃ in the welding heat affected zone is ≥180J, and the transverse DWTT shear area at -25℃ is ≥85%; the longitudinal yield strength can reach 450-550MPa, the longitudinal tensile strength reaches 660-760MPa, and the longitudinal uniform elongation U EL ≥12%, longitudinal yield ratio <0.77, longitudinal stress ratio Rt1.5 / Rt0.5≥1.12, Rt2.0 / Rt1.0≥1.06, the manufactured steel pipe meets the requirements of X80 grade based on strain design. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0054] Figure 1 This is the typical microstructure of the steel plate of Example 3 of the present invention.

[0055] Figure 2 This is a typical precipitation phase of the steel plate of Example 2 of the present invention. DETAILED DESCRIPTION

[0056] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative work all fall within the scope of protection of the present invention.

[0057] Examples 1-8

[0058] This embodiment provides a high-strength pipeline wide and thick steel plate based on strain design and a production method thereof. The chemical composition and weight percentage of the high-strength pipeline wide and thick steel plate are shown in Table 1.

[0059] Table 1 Chemical composition and weight percentage (wt%) of high-strength pipeline wide and thick steel plates of Examples 1-8

[0060]

[0061] The steps include:

[0062] Converter smelting: Add lime and fluorite in a ratio of 4 / 1 to 5 / 1 to form the top slag. Control the weight percentage of FeO+MnO in the slag to ≤1%. The converter tapping temperature is ≤1640°C, the tapping C is ≤0.045%, and the tapping is carried out with slag blocking. The slag layer thickness is ≤40mm. Specific parameters are shown in Table 2.

[0063] Refining outside the furnace: After refining and deoxidation, Ti is added first, followed by Zr and V; the cooling time of the molten steel before loading on the machine is ≥10min;

[0064] Continuous casting: The continuous casting billet casting superheat is 10-40℃, the residence time of the molten steel in the tundish during casting is ≥350s, the dynamic soft reduction of the billet is ≥4mm, the continuous casting adopts a constant casting speed, the casting speed control range is 0.6-1.2m / min, the continuous casting billet center segregation is ≤C0.5 level, the center porosity is ≤0.5 level, and the A / B / C / D type inclusions are controlled within level 1. Specific parameters are shown in Table 3;

[0065] Heating: The continuous casting billet is heated in multiple stages, including preheating, heating, and soaking. The total heating time is 1.0-2.0 min / mm, and the furnace temperature is 1100-1160°C. The specific parameters are shown in Table 4.

[0066] Rolling: includes rough rolling and finishing rolling. Rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The starting temperature of rough rolling is 1070-1130°C, the finishing temperature of rough rolling is 980-1030°C, the total reduction rate of rough rolling is ≥60%, the starting temperature of rough rolling stage 2 is below 1050°C, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases gradually from pass to pass, and the rough rolling speed is 1.0-2.0 m / s. Among them, the last 2-4 passes of rough rolling stage 1, intermediate cooling, and rough rolling stage 2 are all cooled by rapid spray water, with an average cooling rate ≥1°C / s. Specific parameters are shown in Table 4.

[0067] After the rough rolling is completed, the intermediate warm billet is rapidly cooled to 850-900°C, with an average cooling rate of ≥2°C / s, and then warmed to the start temperature of finishing rolling. The deformation rate in the finishing rolling stage is 60-75%, the start temperature of finishing rolling is 790-840°C, and the final rolling temperature of finishing rolling is Ar3±20°C, preferably 730-760°C. The specific parameters are shown in Table 5;

[0068] Cooling: The steel plate is air-cooled for a time of t after rolling. After air cooling, it is pre-straightened and then subjected to two-stage water cooling. The average cooling rate in the first stage is 10-20°C / s, and the average cooling rate in the second stage is 3-10°C / s. The end temperature of water cooling is less than 250°C, preferably 100-200°C. Specific parameters are shown in Table 5.

[0069] The microstructure of the high-strength wide and thick steel plates for pipelines produced in the above-mentioned embodiments is shown in Table 6, and the mechanical properties are shown in Table 7.

[0070] Table 2 Smelting process of Examples 1-8

[0071] Example Steel tapping temperature / ℃ C content of steel produced during smelting / % Top slag lime / fluorite Weight percentage of FeO+MnO in slag / % 1 1629 0.032 4.7 0.92 2 1635 0.039 4.3 0.78 3 1631 0.036 4.2 0.85 4 1621 0.033 4.8 0.95 5 1618 0.027 4.6 0.91 6 1635 0.038 4.2 0.87 7 1626 0.034 4.5 0.94 8 1630 0.037 4.8 0.86

[0072] Table 3 Refining and continuous casting process of Examples 1-8

[0073]

[0074]

[0075] Table 4 Heating and rough rolling process of Examples 1-8

[0076]

[0077] Table 5 Finishing and cooling process of Examples 1-8

[0078]

[0079] Table 6 Microstructure of the steel plates of Examples 1-8

[0080] Example Volume percentage of polygonal ferrite / % Average grain size / μm 1 31 8.2 2 53 7.8 3 65 8.9 4 46 9.4 5 62 7.9 6 58 8.6 7 69 8.3 8 49 8.8

[0081] Figure 2It is a typical precipitation phase of the steel plate of Example 2 of the present invention. It can be seen that fine precipitation with a particle size of less than 20 nm is dispersed in the matrix, which plays a beneficial role in promoting nucleation, refining grains, improving organizational uniformity, and strengthening in the present invention.

[0082] Table 7 Mechanical properties of steel plates of Examples 1-8

[0083]

[0084] Note: The tensile specimen is a full-thickness rectangular specimen with a parallel test section width of 38.1 mm; the impact specimen size is 10*55*55 mm.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength pipeline wide and thick steel plate based on strain design, characterized in that: The chemical composition and its weight percentage are C: 0.030% ~ 0.065%, Si: 0.20% ~ 0.45%, Mn: 1.70% ~ 1.85%, Nb < 0.030%, V: 0.060% ~ 0.15%, (Nb + V): 0.075% ~ 0.170%, Ti: 0.005% ~ 0.025%, Ti / N ≤ 2.0, Ni < 0.15%, Mo < 0.15%, Cr: 0.20% ~ 0.50%, Cu < 0 .15%, (Ni+Mo+Cr+Cu): 0.40%~0.80%, Zr≤0.025%, Al: 0.005%~0.025%, N: 0.005%~0.015%, Ca: 0.0015%~0.0040%, Ca / S≥1.6, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0018%, the balance is iron and unavoidable impurities; the high-strength pipeline wide and thick steel plate CE IIW Controlled at 0.42%~0.49%, CE Pcm Controlled at 0.17% to 0.21%, of which CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; WHAT Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B。 2. The high-strength pipeline wide and thick steel plate based on strain design according to claim 1 is characterized in that: Ti / N: 0.6~1.9, (Ni+Mo+Cr+Cu): 0.40%~0.70%, Ca / S: 1.7~3.

5.

3. The high-strength pipeline wide and thick steel plate based on strain design according to claim 1 or 2, characterized in that: The thickness of the high-strength pipeline wide and thick steel plate is ≥30mm, the microstructure is polygonal ferrite + lath bainite and a small amount of granular bainite, the volume percentage of polygonal ferrite is 20-80%, the grain size is 4-10μm, and fine precipitation with a particle size of <20nm is dispersed in the matrix. The transverse yield strength reaches 490-570MPa, the transverse tensile strength reaches 680-770MPa, the transverse yield strength ratio is <0.78, the average transverse impact energy at -60℃ is ≥220J, the average transverse impact energy at -20℃ of the welding heat affected zone is ≥180J, and the transverse DWTT shear area at -25℃ is ≥85%; the longitudinal yield strength reaches 450-550MPa, the longitudinal tensile strength reaches 660-760MPa, and the longitudinal uniform elongation U EL ≥12%, longitudinal yield strength ratio <0.77, longitudinal stress ratio Rt 1.5 / Rt 0.5 ≥1.12, Rt 2.0 / Rt 1.0 ≥1.

06.

4. The method for producing a high-strength pipeline wide and thick steel plate based on strain design according to any one of claims 1 to 3, characterized in that: The steps include: (1) Heating: The continuous casting billet is heated in multiple stages, including preheating, heating and soaking. The furnace temperature is 1100-1160°C and the total heating time is 1.0-2.0 min / mm. (2) Rolling: including rough rolling and finishing rolling. Rough rolling includes three stages: rough rolling stage 1, intermediate cooling and rough rolling stage 2. The starting temperature of rough rolling is 1070-1130°C, the final rolling temperature of rough rolling is 980-1030°C, the total reduction ratio of rough rolling is ≥60%, wherein the last 2-3 passes of rough rolling stage 1, intermediate cooling and rough rolling stage 2 are all cooled by rapid spray water, the average cooling rate is ≥1°C / s, the starting temperature of rough rolling stage 2 is below 1050°C, the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases gradually, and the rough rolling speed is 1.0-2.0 m / s; After the rough rolling is completed, the intermediate warm billet is quickly cooled to 850-900°C, with an average cooling rate of ≥2°C / s, and then heated to the start temperature of finishing rolling. The deformation rate in the finishing rolling stage is 60-75%, the start temperature of finishing rolling is 790-840°C, and the final rolling temperature of finishing rolling is Ar3±20°C, Ar3=910-273*C-74*Mn-57*Ni-16*Cr-58*Mo-18*Cu; (3) Cooling: The steel plate is air-cooled for a time of t after rolling. After air cooling, it is pre-straightened and then subjected to two-stage water cooling. The average cooling rate in the first stage is 10-20°C / s, and the average cooling rate in the second stage is 3-10°C / s. The end temperature of water cooling is <250°C.

5. The method for producing high-strength pipeline wide and thick steel plates based on strain design according to claim 4, characterized in that: In step (2), the total deformation rate of the two rough rolling stages is 30-50%, and the final rolling temperature is 730-760°C.

6. The method for producing high-strength pipeline wide and thick steel plates based on strain design according to claim 4, characterized in that: In step (3), the air cooling time t = (FRT-Ar3) / a+k*h, t is the air cooling time, s; FRT is the final rolling temperature, °C; a is a coefficient related to the cooling rate, ranging from 0.4 to 1.0 °C / s; k is a coefficient, ranging from 0.9 to 2.0 s / mm, and h is the thickness of the steel plate in mm; the water cooling end temperature is 100 to 200 °C.

7. The method for producing high-strength pipeline wide and thick steel plates based on strain design according to claim 4, characterized in that: The preparation of the continuous casting billet described in step (1) includes converter smelting, refining outside the furnace and continuous casting; the converter tapping temperature of the converter smelting is ≤1640°C, the tapping C is ≤0.045%, the tapping is slag-blocking, and the slag layer thickness is ≤40mm; Ti is added first after refining and deoxidation, and then Zr and V are added; the quenching time of the molten steel before being put on the machine after refining outside the furnace is ≥10min; during the continuous casting process, the continuous casting billet pouring overheat is 10-40°C, the residence time of the molten steel in the tundish during pouring is ≥350s, the dynamic light reduction of the casting billet is ≥4mm, and the continuous casting adopts a constant pulling speed, and the pulling speed control range is 0.6-1.2m / min.

8. The method for producing high-strength pipeline wide and thick steel plates based on strain design according to claim 7, characterized in that: During converter smelting, lime and fluorite are added in a ratio of 4 / 1 to 5 / 1 to form top slag, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

9. The method for producing high-strength pipeline wide and thick steel plates based on strain design according to claim 7, characterized in that: The center segregation of the continuous casting billet is ≤C0.5 level, the center porosity is ≤0.5 level, and the A / B / C / D inclusions are controlled within level 1.

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